New research supports suspicions that mad cow disease can be transmitted through blood transfusions from people who are infected but have not yet developed symptoms.

A team led by Dr F. Houston of the UK Institute for Animal Health reports in this week's Lancet that a healthy sheep can contract bovine spongiform encephalopathy (BSE) by receiving a blood transfusion from an infected sheep.

The infectious agent which causes spongiform diseases in animals also causes variant Creutzfeldt-Jakob disease (vCJD) in humans and sheep provide a good model for the disease in humans.

"Whether the outbreak of variant Creutzfeldt-Jakob disease (vCJD) in the UK will ultimately affect hundreds, or tens of thousands of people, cannot yet be predicted," writes Paul Brown of the US National Institutes of Health in an accompanying editorial. "If large numbers of apparently healthy people are now silently incubating infections with bovine spongiform encephalopathy (BSE), the implications for public health include the possibility that blood from such individuals may be infectious."

Brown describes the evidence that infection can occur through blood transfusions in sheep provided by Houston and colleagues as "convincing". However Brown suggests Houston and colleagues have been too quick to publish with only an experimental result from a single animal. Brown raises concerns about the impact on blood donor programs.

Although Houston and colleagues acknowledge the precautions taken with blood transfusions in the UK and the absence of evidence of vCJD infection through the blood supply, they hope that their findings will help researchers to identify infected cells and test the effectiveness of current blood transfusion precautions.

"We have seen BSE clinical signs and pathological changes in one recipient of blood from a BSE-infected animal," write the researchers. "And we regard this finding as sufficiently important to report now rather than after the study is complete in several years hence."

Australian officials spent the weekend considering the implications of the findings for blood donors and donations.

ABC News reports that blood donations from people who visited Britain during the outbreak of mad cow disease may be banned after a woman in Britain passed on the disease to her unborn baby before she died.

Federal Health Minister Dr Michael Wooldridge will ask the states and territories to impose the ban which is already in place in the US, Austria and New Zealand.

Dr Wooldridge wants the ban as a precaution only and agrees the risk is minimal.

"I think that with the blood supply we should be as precautionary as possible and I would think it wise if people who had a potential exposure to CJD [Creutzfeldt-Jakob disease] were excluded from the blood supply," he said.